GLG 110

Part 1

Chapter 2

Earth Materials and Processes

2.1 The Geologic Cycle

            Shapes the Earth’s surface

Consists of several sub-cycles:

- Tectonic cycle

- Rock cycle

- Hydrologic cycle

- Biogeochemical cycles

The Tectonic Cycle

            Refers to the large-scale geologic processes that Earth’s crust

            Produces landforms such as oceans, continents with mountains

            Driven by forces deep inside the Earth

            Earth’s Lithosphere and Crust:

- Lithosphere: crust and upper-most mantle

- Asthenosphere: layer within the mantle

- Mantle: layer below the crust

- Core: inner-most sphere

Movement of the Lithospheric Plates:

- tectonic (lithospheric) plates: large masses of rocks moving over Earth’s surface

- continental drift

- seafloor spreading

Types of Plate Boundaries:

- convergent (plates colliding)

- divergent (plates separating)

- transform (plates sliding past one another)

Rates of Plate Motion:

- 2 to 15 cm/year

- e.g. San Andreas: about 3.5 cm/year

- in about 20 million years San Francisco and Los Angeles will be next to one another

Pangaea and the Present Continents:

- Pangaea is last super-continent (about 250 million years ago)

- Tethys is most important ocean after splitting of Pangaea into Gondwana and Laurasia

The Tectonic Cycle and Environmental Geology:

- everything on Earth is affected by the tectonic cycle

- plates constantly move

- resources are produced (e.g. oil, gas, coal, minerals)

- global climate patterns are affected

- oceans close and open

- continents shift and change shape and size

- along plate boundaries earthquakes, volcanic eruptions, and mountain belts occur

The Rock Cycle

            Rocks: aggregates of minerals

            Minerals: naturally occurring, inorganic solids with a crystalline structure; they have a certain chemical composition and physical properties

            Three groups of rocks exist:

- Igneous rocks: “fire-formed”; e.g. Granite, Basalt

- Sedimentary rocks: deposited; e.g. Sandstone, Limestone

- Metamorphic rocks: transformed; e.g. Slate, Marble

The Hydrologic Cycle

            Movement of water on the Earth’s surface

            Will discussed more in detail later!         Water is the most important natural resource on Earth!

Biogeochemical Cycles

            Process by which elements are cycled through the atmosphere, lithosphere, hydrosphere, and biosphere

            Tectonic cycle provides energy

            Other cycles are used as storage, and transfer

e.g. carbon cycle (mostly in form of CO₂)

2.2 Rocks

The Strength of Rocks

            Stress: force applied to a rock

Strain: reaction of the rock to stress (e.g. folding, faulting)

Different rocks have different strengths (depending on composition, texture, and location)

Many rocks exhibit fracture systems within them, these are weak areas inside a rock

Types of Rocks

            Igneous rocks: form from magma

- intrusive: form inside the Earth (e.g. Granite), coarse-grained due to slow cooling

- extrusive: form on Earth’s surface (e.g. Basalt), fine-grained due to fast cooling

Sedimentary rocks: form when other rocks weather and erode on or close to Earth’s surface

- detrital: contain grains that traveled (e.g. Sandstone, Shale)

- Bio-chemical: contain grains that fell out of solution (water) (e.g. Limestone, Rock Salt, Gypstone)

Metamorphic rocks: transformed by heat and pressure deep inside Earth

- foliated: minerals aligned in layers due to pressure (e.g. Slate, Schist)

- non-foliated: minerals not aligned in layers due to heat (e.g. Quartzite, Marble)

- chemically active fluids (e.g. water) play important role here

2.3 Surface Processes: Ice and Wind

            Surface processes shape rocks and landforms

            Wind, water, ice are the most important

            Responsible for erosion, transport, deposit of large amounts of earth materials

Ice

Many people live in higher latitudes

Glaciation:

- glacier: land-bound mass of moving ice (continental ice sheets, mountain glaciers)

- glaciers transport and deposit large amounts of rocks

Permafrost:

- is permanently frozen ground

- about 20% of land is permafrost

- continuous permafrost: permanently frozen

- discontinuous permafrost: freezes and thaws seasonally

- very characteristic landforms result from glacial sculpting of the surface (e.g. U-shaped valleys, moraines)

- modern Earth is shaped by last ice-age glaciers (e.g. Great Lakes)

Wind

            Wind blown deposits come in two groups:

- loess (very fine-grained, dust-sized particles)

- sand (fine-grained, in sand dunes)

sand dunes:

- form from sand blown by wind close to surface

- different types of dunes exist: barchan, transverse, parabolic, longitudinal

- dunes migrate and internally layered (slanted layers due to movement)

loess:

- moves in huge dust clouds to altitudes of several thousands of meters

- most dust was produced during last ice ages

- loess is highly susceptible to wind erosion

- loess is relatively stable if compacted and wetted (hydroconsolidation)

Review “Some Questions to Think About” on page 55.